There is a semiconductor device including a memory cell region and a logic circuit region. Memory cells are in the memory cell region, and each memory cell includes a memory capacitor and a transistor. A smoothing capacitor and others are in the logic circuit.
Conventionally, capacitor insulating films which are made of one film are sometimes used for both of a memory capacitor in a memory cell region and a smoothing capacitor in a logic circuit region, when such a semiconductor device is manufactured. In recent years, there has been a demand for a memory capacitor to reduce a thickness of a capacitor insulating film to enable a low-voltage operation, and there has been a demand for a smoothing capacitor to have a capacitor insulating film with a sufficient thickness to suppress a leak current. Thus, it is difficult to use capacitor insulating films which are made of one film for both of a memory capacitor and a smoothing capacitor.
Meanwhile, there is a ferroelectric memory in which a ferroelectric film is used as a capacitor insulating film of a memory capacitor, and a transistor gate structure, in which a silicon oxide film is used as a capacitor insulating film, is adopted for a smoothing capacitor, for example. However, a dielectric constant of a silicon oxide film is significantly lower that a dielectric constant of a ferroelectric film, and it is not possible to achieve sufficient characteristics.
Accordingly, a technique is proposed in which a stack of ferroelectric films is used as a capacitor insulating film of a smoothing capacitor. However, even with this technique, it is difficult to achieve sufficient characteristics with a memory capacitor and a smoothing capacitor.
The problems as above sometimes exist not only in a ferroelectric memory but also in other semiconductor devices such as a DRAM (dynamic random access memory).
Patent Literature 1: Japanese Laid-open Patent Publication No. 2010-10455
Patent Literature 2: Japanese Laid-open Patent Publication No. 2013-168494
Patent Literature 3: Japanese Laid-open Patent Publication No. 10-98169
Patent Literature 4: Japanese Laid-open Patent Publication No. 2002-217381